Air brakes have long been used on heavy duty vehicles for purposes of efficiency and ease of replenishment, since air is always available. In the case of air brakes, pressurized air is used for braking and for preventing vehicles from being moved. In the case of the latter, air brakes prevent vehicle movement by locking the wheels of the vehicle. Such air brakes are set or engaged typically by pulling an air control knob of the air brake plunger outwardly from the dashboard and disengaged by pushing the knob inward or toward the dashboard. Two knobs are typically provided. One knob controls the brakes of the tractor. The other knob controls the brakes of the trailer. The function of the knobs is to control the flow of air for setting or releasing the parking brakes.
One problem with such air brake systems is that the air brake actuation knobs can be tampered with. In order to prevent this type of tampering, devices have been attempted in an effort to disable or prevent each control knob from being actuated.